Synthetic lubricants



nited States Patent SYNTHETIC LUBRICANTS Alfred H. Matuszak, Westfield, and William E. McTurk,

Elizabeth, N. 5., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Application March 17, 1954 Serial No. 416,942

2 Claims. (Cl. 260481) This invention relates to synthetic lubricating compositions. Particularly it relates to synthetic lubricants having utility at both high and low temperatures. More particularly the invention relates to new and improved synthetic lubricants of the ester type which exhibit outstanding characteristics as to pour point and low temperature viscosity.

In the lubricating art, considerable progress has been realized in recent years in the production of lubricants characterized by one or more specific properties and adapted for specific uses. In general, this progress is attributed to two developments, new and improved refining techniques, and addition agents capable of imparting particular properties to available lubricants. Thus, viscosity index improvers and pour point depressors are added to available automotive lubricants to render the lubricants more adaptable to change in temperature conditions. There are, of course, limits upon the range of effectiveness of these addition agents, and certain requirements cannot be met in every instance.

With the development of the turbo-jet and turboprop type aircraft engine, which operate at peak efficiency at extremely high altitudes, there has developed a corresponding need for a lubricant which is efiicacious at the extremely low temperatures encountered at high altitudes. Engine manufacturers and operations personnel dealing with these turbine engines must be supplied with a lubricant possessing exceptionally low viscosities at low temperatures and at the same time having satisfactory lubricating qualities at high temperatures.

The mineral lubricating oils which possess satisfactory low temperature viscosities have generally been found to have flash points that are dangerously low and high temperature viscosities that are below those required. In other words, when the mineral oil isthin enough at low temperatures, it is too volatile at higher temperatures, and in addition is too thin to possess satisfactory lubricity. It has been found that, generally speaking, additive agents do not satisfactorily furnish the required characteristics.

Recently, in an effort to obtain the superior lubricants needed for these turbine type engines, a new field has been explored, namely the synthesis of lubricants from various materials. Esters represent one class of materials which have attracted unusual interest as synthetic lubricants. Esters are generally characterized by high viscosity indices and flash points and lower pour points than mineral oils of a corresponding viscosity. It is with a synthetic lubricant of the ester type that this invention is concerned.

The new synthetic lubricant to which this invention is directed is an ester of a tribasic acid containing combined sulfur which has the following structural formula:

II cm-o-o n t err-b-orw wherein R, R" and R correspond to the alkyl radicals of combining alcohols having from 3 to 10 carbon atoms of branched and/or straight chain configuration. The straight chain alcohols are preferred, however. These alcohols include propyl, butyl, hexyl, octyl, decyl, 2-ethyl butyl, 2-ethyl hexyl, C 0x0 and C Oxo alcohol. Ether alcohol derivatives of ethyl and propyl alcohols such as butoxyethoxy ethanol, isopropoxy ethanol, methoxyisopropoxy isopropyl alcohol, 2-ethylbutoxy ethanol, l-methylhexoxyethoxy ethanol, or mixtures thereof may also be employed.

The carboxy methyl mercapto succinic acid used to form the esters of this invention is readily made by reacting maleic acid and thioglycolic acid. This preparation is straightforward and presents no problems unfamiliar to the art.

The presence of the sulfur atom in the ester of this invention makes them outstanding and extremely interesting, both as a synthetic lubricant and as a blending component for lubricating compositions. The sulfur atom stabilizes the molecule against thermal breakdown. It also serves as an oxygen acceptor thereby preventing oxidative breakdown which is normally due to the presence of peroxides. Thus, the esters of this acid possess a built in thermal stabilizer and oxidation inhibitor.

In addition to this feature the thioether group in the acid structure imparts anti-wear properties and load carrying ability to the ester. These are important properties which are normally obtained through the use of anti-wear or extreme pressure additives. It is exceptional in this instance since in synthetic lubricants the use of extreme pressure or anti-wear additives is generally frowned upon. In service the additive materials may be quickly consumed leaving the lubricant with no anti-wear or load carrying properties. Where these properties are built in, as in the instant compositions, no failure can be attributed to the loss of such desired characteristics because of additive depletion.

Included in the scope of this invention are the various complex esters made from carboxymethyl mercapto-succinic acid (or its partial esters) and polymethylene and polyalkylene glycols such as butane-diol-1,3, butane-diol- 1,4, pentane-diol-1,5 and the di, tri, tetra, etc. ethylene and propylene glycols. The terminus of the complex ester may be either a monobasic acid or a monohydric alcohol as the case may require.

Depending upon the molar ratios of the glycol and the carboxymethylmercapto succinic acid used, various complex ester structures may be obtained. For example, when one mol of the glycol selected is combined with one mol of the mercaptoacid, the following type structure is obtained:

( 1 (Alcohol) mercaptoacid-glycol-monobasic acid When two mols of the glycol are combined with one mol of the mercaptoacid, the following type structure results:

(2) Monobasic acid-glycol-mercaptoacid-glycol-monobasic acid alcohol When one mol of the glycol is combined with two mols of the mercaptoacid, the following type structure is obtained:

(3 (Alcohol) -mercaptoacid-glycol-mercaptoacid- (alcohOl) 2 When three mols of the glycol are combined with one mol of the mercaptoacid, the following type structure results:

(4) (Monobasic acid-glycol) -mercaptoacid It is not definitely known which ofthe available ca:-

O O O R1 R2 wherein R, R R and R are the combining radicals of the alcohols and contain from 3 to 16 carbon atoms, preferably 6 to carbon atoms, each, wherein n is a number from 2 to 10, preferably 2 to 8, and wherein it is a number of from 1 to 10, preferably from 1 to 6.

The alcohols used to form the terminal portions of the complex esters may be either monomeric or dimerized alcohols. They may be of straight or branched chain configuration as described in connection with the simple esters above, and the alcohols used may be alike or diflerent. Particularly desirable are the various 0x0 alcohols formed by the oxonation and hydrogenation of olefins in the OX0 process. These 0x0 alcohols are more fully described in U. S. 2,703,811-Smith.

Operable monobasic acids contain from about 3 to 16 carbon atoms each, of either branched or straight chain configuration. Such acids include butyric, hexanoic, octanoic, decanoic, dodecanoic, tetradecanoic, etc., as well as the various acids derived from the OX0 process, either by caustic fusion of the alcohols obtained or by reacting olefins with carbon monoxide and water.

The instant invention will be more fully explained by reference to the following examples:

EXAMPLE I p The tri-Z-ethylhexyl ester of carboxy methyl mercapto succinic acid was prepared by heating the following ingredients in an esterification apparatus consisting of a oneliter three-necked round bottomed flask equipped with a nitrogen inlet tube, a glass sealed stirrer, a water separator-condenser and a thermometer.

Carboxy methyl mercapto succinic 312.4 g. (1.5 mols).

acid 2-ethyl hexyl alcohol 645.0 g. (4.95 mols). Toluene 200 g. Sodium hydrogen sulfate 7 g.

After heating for 2 hours at 140-145 C. the esterification was complete giving 92 g. of water (81 g. theoretical). The ester-toluene mixture was filtered to remove the catalyst and then distilled at reduced pressure to give a main fraction consisting of 644 g. of a product having the following properties:

To test the load carrying properties of this ester, it was submitted to the shell 4-ball extreme pressure testing machine and gave the following results:

Applied load, kg:

Seizure 110 Weld 160 Wear scar diameter at 60 kg. load, mrn 0.51

These data show this ester to be superior to a commercial type of polyester (Paraplex AP-52) which gives a seizure load of 80 kg, a weld point of 125 ig., and a wear scar diameter of 0.64 mm. at 60 kg. load. This ester is outstandingly superior to conventional dibasic acid esters such as di-Z-ethylhexyl sebacate and di-C 0x0 adipate, which seize at about 50 kg. load and Weld at kg. load, and to polyhydric alcohol esters such as Hercofiex 600 which seizes at about 60 kg. load and welds at 100 kg. load and has a wear scar diameter of 1.68 mm. at 60 kg. load.

EXAMPLE II Following the procedure set out in Example I above a tri-n-hexyl ester of carboxy methyl mercapto succinic acid was prepared. This material gave the following inspections:

Neut. No. (ASTM-D664) -mgm. KOI-I/grm- 0.42

EXAMPLE III Preparation of (C Oxo alcohol) -carboxy methylmercapto succinic acid-PEG ZOO-carboxy methylmercapto succinic acid (0; Oxo alcoho1) (complex ester of 4 mols C 0x0 alcohol, 2 mols of carboxy methylmercaptosuccinic acid, and 1 mol of Polyethylene Glycol of a molecular weight of approximately 200):

Formulation 3 CS acid 626g. 3m. 0 0m alcohol 696 6m. Excess C 010 alcohol 210 Polyethylene glycol 200 285 1.5 m Nev-H804 6.4.1.-.. Heptane l(1Dg Procedure The 906 g. G, OX0 alcohol, 626 g. acid, Nat-ISO; and heptane were heated for 1 hour at -130" C. during which time 100 cc. of water was collected. The 285 g. of polyethylene glycol was then added and the esterification continued at 200 C. for 5 additional hours. Then 3.5 g. of lime was added to neutralize the catalyst (3.0 g. CaO is equivalent to 6.4 g. of NaHSO and promote ester interchange. This was then stripped of alcohol and light ends for 1% hours at ZOO-220 C. to give the complex ester having the following properties:

Kin. vis./2l0 F 9.94 Kin. vis./100 F 75.3 Kin. vis./0 F 8,170 V. I 118 Act. pour pt., F -35 Flash point, P 460 Fire point, F 505 The synthetic lubricating oils of the ester type as de scribed above may be used directly as lubricants or they may be blended with other lubricants such as mineral oils or other synthetic lubricants to obtain many combinations having special characteristics. It may also be desirable to add to the esters various improvers such as viscosity index improvers, such as C acrylate and methacrylate esters and polymers, pour point depressors such as copolymers of fumarate and/or maleate esters with C vinyl esters, etc., oxidation inhibitors, dctergents, corrosion resisting agents and the like.

The complex ester prepared as described in Example III above, a simple diester base stock, and a blend of both, was submitted to the SAEASOD load carrying test. This test is carried out in the conventional SAE Lubricant Tester employing a 3.4:1 gear ratio. After a run-in period of 2 minutes at a 50 lb. load, the load is increased manually by 50 lbs. every seconds until scufiing occurs. Data obtained are set out below:

Lubricant: Test load, lbs. Complex ester of Ex. III 1,450 Di-octyl sebacate 500 Blend of 10 wt. percent of complex ester of Ex. III in di-octyl sebacate 900 It will be seen that small amounts of the complex ester of the invention materially improve the load carrying ability of other synthetic lubricants.

In addition to the di-octyl sebacate ester used above, the complex esters of this invention may be blended with other synthetic lubricating oils. Blends of from about 2.0% to about 50% by weight of the complex ester in such materials as C to C di-esters of adipic, suberic, azeleic or other dibasic acids simple or complex formals, other complex esters, and the like have been found to possess properties that show the advantage of the blend over the base material.

The complex esters as described above may be prepared by methods known to the art. It may be desirable to first prepare the partial ester of the mercapto acid with the alcohol and react the partial ester so formed with the glycol. The glycol may be partially esterified with the monobasic acid and then reacted with the mercaptoacid.

The conditions for the esterification reactions are generally as follows:

Temperature-Of from reflux temperature to about 400 C., preferably 100 to 230 C.

Time.A period of time sufiicient for evolution of theoretical water, usually from 2 to 10 hours.

Catalyst.A catalytic amount of sodium acid sulfate, toluene sulfonic acid, sulfuric acid, etc.

Water entrainer.Between and 40% based on the weight of the glycol of heptane, hexane, toluene, xylene, etc.

It is preferred that the complex esters contain from about to 130 carbon atoms per molecule, preferably from about 30 to 100. For best performance as lubricating compositions they should have ASTM pour points 6 below about 35 F., flash points at least as high as 375 F. and viscosities at 210 F. of between about 2 and 13 centistokes.

This application is a continuation in part of Serial No. 262,475, filed December 19, 1951 and now abandoned, for the same inventors.

What is claimed is:

1. As a synthetic lubricant, a complex ester reaction product having a pour point below 35 F., a flash point above 375 F., and a viscosity at 210 F. in the range of 2 to 13 centistokes, formed by reacting an excess of an alcohol having in the range of 3 to 10 carbon atoms per molecule with carboxy methyl mercapto succinic acid, and then further reacting the ester so formed with a polyethylene glycol having a molecular weight of about 200, the reactions being carried out at a temperature in the range of to 230 C. for a time suflicient for evolution of theoretical water, and said acid, glycol and alcohol being combined in said reaction product in the molar proportions of about 2/1/4.

2. As a synthetic lubricant, the product formed by reacting about 2 moles of carboxy methyl mercapto succinic acid, about 1 mole of polyethylene glycol having a molecular weight of about 200, and about 4 moles of a branched-chain alcohol having about 7 carbon atoms per molecule, said acid being first reacted with an excess of said alcohol in a heptane diluent at a temperature of about 130 C., and the ester so formed then being reacted with said glycol at a temperature of about 200 C., the complex ester so formed being stripped at about 200-220 C. to yield said product having a kinematic viscosity at 210 F. of about 9.94, a viscosity index of about 118, an actual pour point of about -35 F., and a flash point of about 460 F.

References Cited in the file of this patent UNITED STATES PATENTS 2,503,401 Mattano et a1 Apr. 11, 1950 2,576,899 Albrecht Nov. 27, 1951 2,581,514 Chilcote Jan. 8, 1952 2,654,773 Zerbe Oct. 6, 1953 2,737,525 Mulvaney Mar. 6, 1956 

1. AS A SYNTHETIC LUBRICANT, A COMPLEX ESTER REACTION PRODUCT HAVING A POUR POINT BELOW 35*F., A FLASH POINT ABOVE 375*F., AND A VISCOSITY AT 210*F. IN THE RANGE OF 2 TO 13 CENTISTOKES, FORMED BY REACTING AN EXCESS OF AN ALCOHOL HAVING IN THE RANGE OF 3 TO 10 CARBON ATOMS PER MOLECULE WITH CARBOXY METHYL MERCAPTO SUCCINIC ACID, AND THEN FURTHER REACTING THE ESTER SO FORMED WITH A POLYETHYLENE GLYCOL HAVING A MOLECULAR WEIGHT OF ABOUT 200 THE REACTIONS BEING CARRIED OUT AT A TEMPERATURE IN THE RANGE OF 100* TO 230*C. FOR A TIME SUFFICIENT FOR EVOLUTION OF THEORETICAL WATER, AND SAID ACID, GLYCOL AND ALCOHOL BEING COMBINED IN SAID REACTION PRODUCT IN THE MOLAR PROPORTION OF ABOUT 2/1/4. 